Valve mechanism for multi-cylinder internal combustion engine and assembling method of valve mechanism therefor

ABSTRACT

Valve mechanism for a multi-cylinder internal combustion engine and iassembling method of the valve mechanism therefor are disclosed in which a swing camshaft is selectively assembled for each of the cylinders on the basis of at least an inner diameter of an inserting hole of the swing camshaft to make a lift difference between two engine valves (for example, two intake valves per cylinder) which is involved in a radial inclination of the swing camshaft with respect to a supporting shaft such as a drive shaft uniform between each of the cylinders.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a valve mechanism for a multi-cylinder internal combustion engine in which operational states such as valve lift quantities of engine valves which correspond to intake valves or exhaust valves and such as working angles of the engine valves are controllable in accordance with a driving condition of the engine and, especially, relates to the valve mechanism for the multi-cylinder internal combustion engine and assembling method of the valve mechanism therefor in which a dispersion (or a variation) of an inclination quantity (degree) of a swing camshaft having two swing cams per cylinder with respect to a supporting shaft between each of the cylinders is reduced to make the valve lift quantities of the engine valves substantially uniform between each of the cylinders.

(2) Description of Related Art

A Japanese Patent Application Publication (tokkai) No. 2004-060635 published on Feb. 26, 2004 (which corresponds to a U.S. Pat. No. 6,694,935 issued on Feb. 24, 2004) exemplifies one of previously proposed valve mechanisms for the multi-cylinder internal combustion engines. The previously proposed valve mechanism described in the above-identified Japanese Patent Application Publication includes: a drive shaft on an outer periphery of which a drive cam is installed and to which a rotating force (a torque) of a crankshaft of the engine is transmitted; a transmitting mechanism which converts the rotating force transmitted from the drive cam into a swing motion; a pair of swing cams which swing through a rocker arm of the transmitting mechanism to open and close two intake valves per cylinder via respective valve lifters: and a lift variable mechanism which varies the valve lift quantities and the working angles of the respective intake valves in accordance with the engine driving condition.

This lift variable mechanism is provided with control cams for each of the cylinders on an outer periphery of a single control shaft rotationally controlled by means of a control mechanism. The rotational control of each control cam causes a posture of the transmitting mechanism such as the rocker arm to be varied. Thus, a valve lift characteristic of each of the intake valves is varied via each of the swing cams.

The respective swing cams are integrally installed on both end portions in an axial direction of cylindrical swing camshaft rotatably penetrated through an outer periphery of the drive shaft via an internal inserting hole. A cam surface provided on each lower surface of the swing cams slides on an upper surface of the valve lifter so that each intake valve is operated to be open or closed.

SUMMARY OF THE INVENTION

In the previously proposed valve mechanism described in the above-identified Japanese Patent Application Publication, the valve lift quantity of each of the intake valves is variably controlled through the lift variable mechanism so that a performance of the engine can sufficiently be enhanced. However, due to the dispersion of a clearance provided between an inner peripheral surface of the inserting hole of the swing camshaft and an outer peripheral surface of the drive shaft which is developed during a manufacturing (assembling) of the engine, each engine valve is often operated with the swing camshaft inclined on the drive shaft. If the valve mechanism described in the above-identified Japanese Patent Application Publication is operated with the swing camshaft inclined as described above, a cam lift quantity of each swing cam with respect to each of the valve lifters is also varied so that the dispersion in the valve lift quantities of the respective intake valves becomes easy to occur. Furthermore, when the dispersion of the inclination quantity (degree) of the swing camshaft occur between each of the cylinders, a performance of the engine is reduced.

Especially, during performing a small valve lift control, the dispersion in the valve lift quantity produces a large influence on the engine performance.

It is, hence, an object of the present invention to provide a valve mechanism for a multi-cylinder internal combustion engine and an assembling method of the valve mechanism for the multi-cylinder internal combustion engine which can prevent a reduction in the engine performance, with a valve lift difference between two engine valves made uniform between each of the cylinders by making an inclination quantity of the swing camshaft uniform between each of the cylinders in order to decrease the dispersion of the inclination quantity of the swing camshaft between each of the cylinders.

According to one aspect of the present invention, there is provided a valve mechanism for a multi-cylinder internal combustion engine, comprising: a drive shaft rotationally driven by means of a crankshaft of the engine and on an outer periphery of which a drive cam is installed; a swing camshaft swingably and axially supported on an outer periphery of a supporting shaft via an inserting hole thereof with a predetermined clearance and on outer peripheries of axial both end portions of which two swing cams per cylinder are installed; two engine valves operated to be open and closed by taking swing motions of the two swing cams via the swing camshaft; and a transmitting mechanism linked to one axial end portion of the swing camshaft to convert a rotational motion of the drive cam into the swing motion to transmit the swing motion to the two swing cams, wherein the swing camshaft is selectively assembled for each of the cylinders on the basis of at least an inner diameter of the inserting hole to make a lift difference between the two engine valves which is involved in a radial inclination of the swing camshaft with respect to the supporting shaft uniform between each of the cylinders. According to the one aspect of the present invention, the inclination quantity of the swing camshaft can be uniformized (made uniform) between each of the cylinders so that the dispersion of the valve lift difference of the two engine valves between each of the cylinders can be reduced. Thus, the engine performance and engine stability can be improved.

According to another aspect of the present invention, there is provided an assembling method of a valve mechanism for a multi-cylinder internal combustion engine, the valve mechanism comprising: a drive shaft rotationally driven by means of a crankshaft of the engine and on an outer periphery of which a drive cam is installed; a swing camshaft swingably and axially supported on an outer periphery of a supporting shaft via an inserting hole thereof with a predetermined clearance and on outer peripheries of axial both end portions of which two swing cams per cylinder are installed; two engine valves operated to be open and closed by taking swing motions of the two swing cams via the swing camshaft; and a transmitting mechanism linked to one axial end portion of the swing camshaft to convert a rotational motion of the drive cam into the swing motion to transmit the swing motion to the two swing cams, and the assembling method comprising: measuring an outer diameter of the supporting shaft and an inner diameter of the inserting hole of the swing camshaft; and selectively assembling the swing camshaft for each of the cylinders on the basis of the measured inner diameter of the inserting hole to make a lift difference between the two engine valves which is involved in a radial inclination of the swing camshaft with respect to the supporting shaft uniform between each of the cylinders.

According to a still another aspect of the present invention, there is provided an assembling method of a valve mechanism for a multi-cylinder internal combustion engine, the valve mechanism comprising: a drive shaft rotationally driven by means of a crankshaft of the engine and on an outer periphery of which a drive cam is installed; a swing camshaft swingably and axially supported on an outer periphery of a supporting shaft via an inserting hole thereof with a predetermined clearance and on outer peripheries of axial both end portions of which two swing cams per cylinder are installed; two engine valves operated to be open and closed by taking swing motions of the two swing cams via the swing camshaft; and a transmitting mechanism linked to one axial end portion of the swing camshaft to convert a rotational motion of the drive cam into the swing motion to transmit the swing motion to the two swing cams, and the assembling method comprising:

-   measuring an outer diameter of the supporting shaft and an inner     diameter of the inserting hole of the swing camshaft; and     selectively assembling the transmitting mechanisms whose lengths are     different from each other onto the swing camshaft for the respective     cylinders on the basis of the measured inner diameter of the     inserting hole to make a lift difference between the two engine     valves which is involved in a radial inclination of the swing     camshaft with respect to the supporting shaft uniform between each     of the cylinders.

This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features. The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an essential part perspective view of a V-type six-cylinder engine to which a valve mechanism for a multi-cylinder internal combustion engine in a first preferred embodiment according to the present invention is applicable.

FIG. 2 is a plan view representing the essential part of the valve mechanism located at a three-cylinder side of one of two banks of the six-cylinder internal combustion engine shown in FIG. 1.

FIG. 3 is a cross sectional view representing an inclination state of a swing cam assembly in a low engine revolution area.

FIG. 4 is a cross sectional view representing another inclination state of the swing cam assembly in a high engine revolution area.

FIGS. 5A and 5B are side views of the valve mechanism shown in FIG. 1 which are viewed from an arrow A-marked direction thereof and representing a valve closure action during a minimum lift control and representing a valve open action during the same minimum lift control, respectively.

FIGS. 6A and 6B are side views of the valve mechanism in FIG. 1 viewed from the arrow A-marked direction and representing the valve closure action during a maximum lift control and representing the valve open action during the same maximum lift control, respectively.

FIGS. 7A, 7B, 7C, and 7D are valve lift characteristic graphs of respective intake valves of respective cylinders in the low engine revolution area and FIGS. 7A′, 7B′, 7C′, and 7D′ are valve lift characteristic graphs of the respective intake valves of respective cylinders in the high engine revolution area.

FIG. 8 is a perspective view of an essential part of the valve mechanism in a second preferred embodiment of the valve mechanism according to the present invention.

FIG. 9 is a flowchart representing an assembling procedure of each component executed in the second embodiment.

FIGS. 10A and 10B are valve lift characteristic graphs of the respective intake valves in the low revolution area and in the high engine revolution area on the basis of a lift difference of each of swing cams in a third preferred embodiment of the valve mechanism according to the present invention, respectively.

FIGS. 11A and 11B are cross sectional views of an essential part of the valve mechanism representing a cam clearance between each of the swing cams and each valve lifter in a fourth preferred embodiment of the valve mechanism according to the present invention.

FIG. 12 is a cross sectional view representing an essential part of the valve mechanism in a fifth preferred embodiment according to the present invention.

FIG. 13 is a valve lift characteristic of the valve mechanism in a sixth preferred embodiment according to the present invention.

FIG. 14 is a correlation diagram of a rotational angle of a control shaft and a valve lift quantity of a control shaft of the valve mechanism in the sixth preferred embodiment according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a valve mechanism for a multi-cylinder internal combustion engine and its assembling method thereof will be described in details with reference to the drawings in order to facilitate a better understanding of the present invention.

In each of these preferred embodiments, the valve mechanism is applicable to a V-type six-cylinder internal combustion engine. In FIGS. 1 and 2, the present invention is applicable to three cylinders belonging to one of two opposite banks of the V-type six-cylinder internal combustion engine. A cylinder sequence is such that a rightmost position (a most forward end side) as viewed from FIG. 2 indicates a first cylinder (No. 1 cylinder), a center position as viewed from FIG. 2 indicates a second cylinder (No. 2 cylinder), and a leftmost side (a most rear end side) as viewed from FIG. 2 indicates a third cylinder (No. 3 cylinder).

That is to say, the valve mechanism is, as shown in FIGS. 1 and 2 and as shown in FIGS. 5A, 5B, 6A, and 6B, includes: two intake valves 2 a, 2 b per cylinder biased in their closure directions thereof by means of valve springs 3 a, 3 b and installed to be enabled to swing (swingably installed) via valve guides (not shown); a varying mechanism 4 variably controlling a valve lift (valve lift quantity) and a working angle of each intake valve 2 a, 2 b; a control mechanism 5 which controls an operational position of varying mechanism 4; and an actuator 6 which rotationally (or rotatably) drives control mechanism 5.

Varying mechanism 4 includes: a hollow drive shaft 13 rotatably supported on a bearing 14 (refer to FIG. 5A) provided on an upper part of cylinder head 1; a single drive cam 15 per cylinder fixed by means of a fixture pin on drive shaft 13; a swing cam assembly 17 swingably supported on an outer peripheral surface of drive shaft 13 and slidably contacted on each of upper surfaces of valve lifters 16 a, 16 b to operate to open intake valves 2 a, 2 b; and a transmitting mechanism interlinked between drive cam 15 and swing cam assembly 17 to transmit the rotating force of drive cam 15 as a swing force of swing cam assembly 17.

Drive shaft 13 is formed in a hollow tubular shape and is arranged along a forward-and-rearward direction of the engine. In addition, a rotating force (or torque) is transmitted from a crankshaft of the engine to drive shaft 13 via a timing chain wound on a driven sprocket 7 installed on one end portion of drive shaft 13 (refer to FIG. 2), the direction of the rotating force being set in an arrow-marked direction at a position of drive shaft 13 in FIG. 1.

An oil passage 13 a via which lubricating oil is supplied from a main oil gallery (not shown) toward an inner axial direction of drive shaft 13 is formed along the inner axial direction thereof.

Bearing 14 is, as shown in FIG. 5A, provided with a main bracket 14 a arranged on cylinder head 1 to rotatably support drive shaft 13 via a swing camshaft 18 which will be described later and a sub bracket 14 b installed on an upper end portion of main bracket 14 a to rotatably support a control shaft 32 which will be described later. Both brackets 14 a, 14 b are tightened commonly to each other with a pair of bolts 14 c, 14 c from an upper direction as viewed from FIG. 5A.

it should be noted that drive cam 15 has a cam main body having an axial center Y offset from an axial center X of drive shaft 13 in a radial direction by a predetermined quantity.

Swing cam assembly 17, as shown in FIGS. 1 through 4, includes: cylindrical swing camshaft 18 rotatably fitted onto an outer peripheral surface 13 b of drive shaft 13 which serves as a supporting shaft; and a pair of first and second swing cams 19 a, 19 b integrally installed on both end portions of swing camshaft 18 in the axial direction of swing camshaft 18 at a predetermined interval (of distance). Swing cam assembly 17 is swingably supported on drive shaft 13 through swing camshaft 18.

An inserting hole 18 a through which drive shaft 13 is inserted is penetrated through an inner part of swing camshaft 18 and a journal portion 18 b rotatably journalled on main bracket 14 a is integrally formed on an approximately center position in the axial direction of an outer peripheral surface of swing camshaft 18.

Inserting hole 18 a is formed with a first annular groove 20 a at an approximately center position of this hole 18 a in the axial direction of the inner peripheral surface thereof and a pair of second annular grooves 20 b, 20 b are formed on both sides of first annular groove 20 a, each of second annular grooves 20 b, 20 b being spaced apart by a predetermined interval of distance from first annular groove 20 a.

A width (length) of first annular groove 20 a in the axial direction of swing camshaft 18 is relatively small (narrow or short) and is set to be smaller (narrower or shorter) than the width (length) of each of pair of second annular grooves 20 b, 20 b. On the other hand, pair of second annular grooves 20 b, 20 b are formed symmetrically in left and right sides with a center line Q (shown in FIG. 3) located in the axial direction of swing camshaft 18 as a center.

In addition, a pair of first journal surfaces 21 a, 21 a are formed at both side surfaces of first annular groove 20 a located on the inner peripheral surface of inserting hole 18 a. In addition, a pair of second journal surfaces 21 b, 21 b are formed at left and right outer sides of pair of second annular grooves 20 b, 20 b, viz., at both end portions of inserting hole 18 a in the axial direction of inserting hole 18 a. Journal portion 18 b described above is formed at a position of the outer peripheral surface of swing camshaft 18 avoiding positions of second annular grooves 20 b, 20 b in a state where journal portion 18 b is extended over first journal surfaces 21 a, 21 a.

First and second swing cams 19 a, 19 b are formed in droplet forms and have cam nose portions extended toward their tips and cam surfaces 22 a, 22 b are respectively formed on the respective lower surfaces of first and second swing cams 19 a, 19 b.

Each of cam surfaces 22 a, 22 b includes a base circle surface located at swing camshaft 18 and a lift surface extending in an arc shape from the base circle surface toward the cam nose portion. This lift surface is constituted by a ramp portion located at the base circle surface and a lift portion extended from the ramp portion to a maximum lift summit surface provided on the tip of the cam nose portion.

A pin hole 19 c through which a pin 28 to couple with another end portion 25 b of a link rod 25 which will be described later is inserted is penetrated through first swing cam 19 a at cam nose portion side of the tip portion thereof. In addition, a forward-and-rearward direction of an upper surface of first swing cam 19 a is formed more strongly than second swing cam 19 b to secure a rigidity to receive large loads from a swing motion force from link rod 25, spring forces of valve springs 3 a, 3 b, and so forth.

The transmitting mechanism includes: a rocker arm 23 arranged for each of the cylinders at the upper side of drive shaft 13; a link arm 24 to interlink each one end portion 23 a of each corresponding one of rocker arms 23 with each of drive cams 15; and link rod 25 to interlink each other end portion 23 b of each rocker arm 23 with first swing cam 19 a.

Rocker arm 23 described above is rotatably supported on a control cam 33 which will be described later via a supporting hole 23 c formed on an inner part of a cylindrical base portion provided at the center of rocker arm 23. In addition, a pin 26 is projected at one end portion 23 a of rocker arm 23 projected from the cylindrical base portion in a single direction and a pin hole into which a pin 27 to link with one end portion of link rod 25 is fitted is formed on other end portion 23 b of rocker arm 23.

Link arm 24 includes a relatively large-diameter annular base portion 24 b projected at a predetermined position of an outer peripheral surface of base portion 24 a. A fitting hole to rotatably fit a cam main body of drive cam 15 is formed at a center position of base portion 24 a. A pin hole through which pin 26 is rotatably inserted is penetrated at projection end 26 b.

Link rod 25 is formed approximately in a Japanese letter of < in a recess shape faced toward rocker arm 23. Pin inserting holes through which the other end portion 23 b of rocker arm 23 and the end portions of respective pins 27, 28 inserted through respective pins of cam nose portion of first swing cam 19 a are penetrated at both end portions 25 a, 25 b.

Control mechanism 5 includes: control shaft 32 rotatably supported on the same bearing 14 at the upper position of drive shaft 13; and control cam 33 integrally installed on an outer peripheral surface of control shaft 32 and which provides a swing fulcrum of rocker arm 23.

Control shaft 32 is disposed in parallel to drive shaft 13 in the forward-and-rearward direction of the engine and a journal portion at a predetermined position thereof is rotatably journalled between main bracket 14 a of bearing 14 and sub bracket 14 b of bearing 14.

Control cam 33 is installed for each cylinder, namely, for each rocker arm 23 and is approximately eccentric annularly formed and a position of an axial center P2 of control cam 33 is offset by a predetermined quantity (distance) from an axial center P1 of control shaft 32.

Drive mechanism 6, as shown in FIG. 1, includes: a housing (not shown) fixed at the rear end portion of cylinder head 1: an electric motor 35 fixed at one end portion of the housing; and a ball screw transmitting mechanism 36 installed within an inner part of the housing for transmitting a rotating driving force of electric motor 35 to control shaft 32.

Electric motor 35 is constituted by a proportional type DC motor and is driven in response to a control signal from a control unit 38 which detects a driving condition of the engine.

This control unit 38 feeds back detection signals from various sensors such as a crank angle sensor 39, an airflow meter 40, a coolant temperature sensor 41, and a potentiometer 42 which detects a rotation position of control shaft 32 to detect a present engine driving condition through a calculation thereof and so forth and outputs a control current to electric motor 35.

Ball screw transmitting mechanism 36 mainly includes: a ball screw shaft 43 arranged coaxially with a drive shaft of electric motor 35 within the housing; a ball nut 44 which is a movement nut meshed with an outer periphery of ball screw shaft 43; a linkage arm 45 coupled along a diameter direction at one end portion of control shaft 32; and a link member 46 which is interlinked between linkage arm 45 and ball nut 44.

Then, an axial directional movement force is provided for ball nut 44 while a rotational motion of ball screw shaft 43 is converted via each ball into a linear motion.

Hereinafter, an action of the first embodiment will briefly be described. First, for example, in the low engine revolution driving area including an idling of the engine, electric motor 35 drivingly rotates ball screw shaft 43 in a single direction through a control current from control unit 38. At this time, along with this rotation, each ball is rolled moved between a ball circulation groove and a guide groove and ball nut 44 is accordingly moved linearly in a single direction.

Thus, control shaft 32 is, as shown in FIGS. 5A, 5B, drivingly rotated in a counterclockwise direction with a link member 46 and an linking arm 45 so that control cam 33 is rotated with the same radius around an axial center P1 of control shaft 32. Thus, a thickness portion of control Shaft 32 becomes spaced apart in the upper direction from drive shaft 13 and is moved therefrom. Thus, the other end portion 23 b of rocker arm 23 and a fulcrum point of link rod 25 are moved in the upper direction with respect to the driving shaft 13. Therefore, a cam nose side of each swing cam 19 a, 19 b is forcefully pulled up via link rod 25 so that the whole cam is pivoted in a clockwise direction.

Then, when drive cam 15 is rotated to push up one end portion 23 a of rocker arm 23 via link arm 24, its lift quantity (lift distance) is transmitted to respective swing cams 19 (19 a, 19 b) and valve lifters 16 a, 16 b. However, lift quantities L1 become sufficiently small.

Hence, in the low engine revolution area, the valve lift quantity becomes the smallest. Hence, a valve open timing of each intake valve 2 (2 a, 2 b) becomes retarded and a valve overlap with the exhaust valves becomes minor. Thus, an improvement in the fuel economy and a stable revolution of the engine can be achieved.

In addition, in a case where the engine driving condition is transferred to the high engine revolution area, electric motor 36 is reversely revolved in response to the control signal from control unit 38 in order for ball screw shaft 43 to be drivingly rotated in the same direction. Hence, ball nut 44 linearly moves in the other direction via each ball. Thus, control shaft 32 pivots control cam 33 from a position denoted by FIGS. 5A and 5B in the clockwise direction so that axial center P2 is pivoted in the downward direction, as shown in FIGS. 6A and 6B. Therefore, whole rocker arm 23 is, in turn, moved toward drive shaft 13 and its other end portion 23 b pushes the cam nose portion of swing cam 19 a downward via link rod 25 so that the whole of each swing cam 19 a, 19 b is pivoted by a predetermined quantity in the counterclockwise direction.

Then, when drive cam 15 is rotated so as to push upward one end portion 23 a of rocker arm 23 via link arm 24, its lift quantity is transmitted to first and second swing cams 19 a, 19 b and valve lifters 16 a, 16 b via link rod 25. The valve lift quantity becomes accordingly increased.

Thus, in the above-described high engine revolution area, a valve lift quantity L2 of each intake valve 2 becomes maximally large (long) so that a valve opening timing of each intake valve 2 (2 a, 2 b) becomes earlier but the valve closure timing becomes retarded. Consequently, an intake air charging efficiency is improved so that a sufficient output (power) can be secured.

It should be noted that, during above-described engine revolution areas of engine driving, due to spring forces of valve springs 3 a, 3 b and a pressing force of link rod 25, swing camshaft 18 is inclined in a radial direction thereof with respect to drive shaft 13. Consequently, such a problem that a difference in the lift quantity between each intake valve 2 a, 2 b is developed is raised.

Hereinafter, causes of the inclination of swing camshaft 18 will be explained on the basis of FIGS. 3 and 4. First, the inclination of swing camshaft 18 in the low engine revolution area will be described on the basis of FIG. 3. When one end portion of swing camshaft 18 is pressed in the downward direction with link rod 25 by a force having a load of FL via the cam nose portion of first swing cam 19 a, this pressing down force causes both of swing cams 19 a, 19 b to be operated to open respective intake valves 2 a, 2 b via respective valve lifters 16 a, 16 b. On the other hand, at the same time, spring loads FS1, FS2 of respective valve springs 3 a, 3 b are acted upon respective swing cams 19 a, 19 b via valve lifters 16 a, 16 b in the upper direction.

A load vector FS1 of valve spring 3 a acted upon first swing cam 19 a is acted as an upward load along the approximately axial direction of link rod 25. Hence, load vector FS1 is overlapped on the direction of load FL acted from link rod 25. Hence, almost no inclination moment on swing cam shaft 18 is acted from first swing cam 9 a.

On the other hand, spring load FS2 of valve spring 3 b is acted upon second swing cam 19 b similarly. Since first swing cam 19 a is separated from second swing cam 19 b by a long distance of L, a larger inclination moment FS2×L is acted upon second swing cam 19 b in the counterclockwise direction.

It should be noted that a relation between a valve lift Y1 of intake valve 2 a at the one side (link rod side) and a valve lift Y2 of intake valve 2 b at the other side is Y1>Y2 and an equation of ΔY=Y1−Y2 is resulted. This means that the lift of one side intake valve 2 a is larger than that of the other side intake valve 2 b by a lift ΔY.

Then, it should be noted that an inclination angle of swing camshaft 18 is determined according to a clearance ΔD between an inner diameter E (inner peripheral surface) of an inserting hole 18 a of swing camshaft 18 and an outer diameter F (an outer peripheral surface) of drive shaft 13. That is to say, if the bearing width of swing camshaft 18 is S, ΔY≈ΔD×L/S.

Herein, it should also be noted that inner diameter (inner peripheral surface) E of inserting hole 18 a and outer diameter (outer peripheral surface) F of drive shaft 13 have respective dispersions during a manufacturing (assembling) process. Hence, clearance ΔD is dispersed between the respective cylinders. This makes ΔY dispersed between the respective cylinders. Hence, the flow rate of air mixture fuel is dispersed for each cylinder. Consequently, the combustion state is dispersed, the intake air charging efficiency is dispersed between each cylinder, and, thus, a performance of the engine is reduced and an un-stabilization of engine revolutions is introduced.

Next, the inclination of swing camshaft 18 in the high engine revolution area will be described on the basis of FIG. 4. In this high engine revolution area, as a load acting upon each swing cam 19 a, 19 b, an influence of inertia forces FI of swing cams 19 a, 19 b becomes larger than spring loads FS of valve springs 3 a, 3 b.

That is to say, swing cam inertia load FI1 is acted upon first swing cam 19 a and spring load FS1 of one side valve spring 3 a is similarly acted upon first swing cam 19 a in the case of the low engine revolution area. Hence, a load expressed as FI1-FS1 is acted in the downward direction along the axial direction of link rod 25. However, almost no inclination moment is acted on swing camshaft 18.

On the other hand, swing cam inertia load FI2 is acted similarly on second swing cam 19 b and spring load FS2 of valve spring 3 b is acted in the opposite direction.

Hence, a load of FI2-FS2 is acted in the downward direction. A point of application is separated by a length of L. Thus, second swing cam 19 b receives a large inclination moment {(FI2−FS2)×L}. A moment direction thereof is the clockwise direction which is opposite to a case of FIG. 3 in the low engine revolution area.

As a result of this, swing camshaft 18 is inclined in the clockwise direction and a lift difference ΔZ between two intake valves 2 a, 2 b is developed. It should be noted that the inclination angle is determined according to inner diameter E of inserting hole 18 a of swing camshaft 18 and outer diameter F of drive shaft 13. However, inner diameter E and outer diameter F have dispersions developed during the manufacturing (assembling) process. This ΔD is dispersed between each of the cylinders. This makes ΔY in the low engine revolution area dispersed and makes ΔZ in the high engine revolution area dispersed. Hence, the flow rate of the air mixture fuel for each cylinder is dispersed. The intake air charging efficiencies are dispersed between respective cylinders. Consequently, the reduction of the engine performance and the un-stabilization of the revolutions are introduced.

Therefore, in this embodiment, a technical problem due to the dispersion in the lift quantities between respective intake valves 2 a, 2 b due to the (radial) inclination of swing camshaft 18 has solved in the following way.

FIGS. 7A through 7D′ show characteristics of the lift quantity of each intake valve 2 a, 2 b at first through third cylinders (No. 1 through No. 3) of one of the two opposite banks of the V-type multi-cylinder engine. In each of FIGS. 7A through 7D′, a bold hatch portion at each of left sides in respective drawings of FIGS. 7A through 7D′ denotes the valve lift quantity of intake valve 2 a at one side swing cam (first swing cam) 19 a, a thin hatch portion at each of right sides in respective drawings denotes the valve lift quantity of intake valve 2 b at the other side swing cam (second swing cam) 19 b. In addition, FIGS. 7A through 7D show the case of the low engine revolution area and FIGS. 7A′ through 7D′ show the case of the high engine revolution area. In these examples, a case where swing cam assembly 17 at the third cylinder (No. 3 cylinder) is selected is shown.

Now, an example where the inclination of swing camshaft 18 is large will herein be explained. For example, in a case where the above-described clearance E1-F1 in a case of first cylinder (No. 1 cylinder), viz., ΔD (ΔD1) is 25 μm and ΔD (ΔD2) in the second cylinder (No. 2 cylinder) is 22 μm, a clearance difference (the dispersion of the clearance) between both first (No. 1) and second (No. 2) cylinders is small. Lift difference ΔY of both intake valves 2 a, 2 b in the low engine revolution area is, for example, ΔY1 at the first cylinder (No. 1 cylinder) is 19 μm and ΔY2 at the second cylinder (No. 2 cylinder) is 17 μm from the equation of ΔY≈ΔD×L/S.

However, ΔD3 at the third cylinder side (No. 3 cylinder) has the clearance of E3-F3 of 50 μm. If such a large clearance as 50 μm is present, ΔD3 at the third cylinder side, in this case, is larger those of any other cylinders. ΔY3 in this case is 38 μm which is larger than those of any other cylinders. Hence, the combustion state in the third cylinder is different from the other cylinders. In view of the multi-cylinder engine, there is a possibility that an engine performance is reduced and the engine revolutions become unstable.

Therefore, if swing cam assembly 17 for the third cylinder is selectively replaced with another swing cam assembly 17 in which inner diameter E of inserting hole 18 a of swing cam 18 is relatively small, namely, ΔD1 and ΔD2 are approximately the same and ΔD3 is replaced with ΔD3′ at the third cylinder side, namely, (E3-F3) is replaced with (E3′-F3) of 24 μm (a portion of third cylinder shown in FIG. 7B). At this time, ΔY3′ indicates 18 μm so that the substantially same lift difference as ΔY1 and ΔY2 is obtained at the third cylinder and substantially the same valve lift quantity for each of intake valves 2 a, 2 b is obtained in the third cylinder.

Thus, the large dispersion of the lift difference between each intake valve 2 a, 2 b between each of the respective cylinders can be suppressed. Consequently, the performance of the multi-cylinder internal combustion engine can be improved and the stabilization of the revolutions can be achieved.

Next, the lift difference between the two intake valves in the high engine revolution area will herein be considered. In this high engine revolution area, as described hereinabove, the influence of an inertia force due to loads of cam nose portions of first and second swing cams 19 a, 19 b become larger than the influence of spring loads of valve springs 3 a, 3 b. Hence, the inclination direction of swing camshaft 18 is reversed (refer to FIG. 4).

That is to say, as denoted by a portion of first cylinder in FIG. 7D′, lift difference ΔZ1 (19 μm) between each of intake valves 2 a, 2 b is developed due to ΔD1 which is a difference between each of inner and outer diameters E1-F1 at the first cylinder side. The lift of intake valve 2 a at first swing cam 19 a becomes lower. As described before, ΔD2 (22 μm) which is the difference between the inner and outer diameters (E2-F2) at the second cylinder is approximated (near) to ΔD1 (25 μm) which is the difference (E1-F1) of the inner and outer diameters at the first cylinder. Therefore, the lift differences ΔZ2 (17 μm) of each intake valve 2 a, 2 b at the second cylinder is a value approximated to each other.

In the third cylinder, difference (E3-F3) in the inner and outer diameters described above is as excessively large as ΔD3 (50 μm), lift difference ΔZ3 between each intake valve 2 a, 2 b indicates 38 μm.

Hence, the selective assembly of swing cam assembly 17 (swing camshaft 18) as described above is carried out for the third cylinder so that lift difference ΔZ3′ indicates 18 μm which is approximately same as above-described first cylinder and second cylinder which have approximately the same lift difference value.

Hence, if the selective assembly for the swing cam assembly 17 (swing camshaft 18) is carried out, it becomes possible to make the lift difference between the two valves uniform for both of the low and high engine revolution areas between each of the cylinders.

Next, an engine intermediate revolution area will be considered. For example, when the number of engine revolutions are reduced from the high engine revolution area, the inertia force of the cam nose portion of second swing cam 19 b becomes reduced. Hence, as shown in FIG. 4, swing camshaft 18 receives a moment in the clockwise direction so as to gradually become float from a state in which a right upper end portion of swing camshaft 18 is edge stricken on the outer peripheral surface of swing camshaft 18. That is to say, as the number of revolutions becomes reduced, swing camshaft 18 is gradually inclined in the counterclockwise direction and the inclination angle becomes reduced.

Then, when the engine revolutions become the intermediate revolutions, the inclination of swing camshaft 18 is almost nullified (eliminated) and the swing camshaft 13 is approximately in parallel to drive shaft 13. If, furthermore, the number of engine revolutions is reduced, the inclination in the reverse direction occurs. At last, the inclination state shown in FIG. 3 is found. That is to say, swing camshaft 18 receives the moment in the counterclockwise direction and a left upper end portion of swing camshaft 18 is struck on an edge of an outer peripheral surface of drive shaft 13.

In this case, if difference ΔD between inner diameter E of inserting hole 18 a and outer diameter F of drive shaft 13 in each of the cylinders is made uniform, the large difference between each of the cylinders in the lift difference between each intake valve 2 a, 2 b can be suppressed.

As described above, in the valve mechanism in the first preferred embodiment, the large dispersion of the lift difference between respective intake valves 2 a, 2 b can be suppressed between each of the cylinders irrespective of the engine revolutions. A stabilization of combustion in the multi-cylinder internal combustion engine can be achieved and the engine performance can be improved.

It should be noted that an object to be the selective assembly may be considered not for swing cam assembly 17 but for the assemble of drive shaft 13. However, since this drive shaft 13 is a single shaft for three cylinders, a value of an axial diameter (outer diameter) F is relatively stable at each of the three inserting positions of respective swing camshafts 18 of the three cylinders. Hence, a necessity of the selective assembly for this drive shaft 13 is low. It should, however, be noted that inner diameters E (E1, E2, E3) of inserting hole 18 a of swing camshafts 18 so as to make equal lift difference ΔD (ΔD1, ΔD2, and ΔD3) for the three cylinders with axial diameters F of drive shafts 13 of the three inserting positions measured, respectively, may be selected.

It should also be noted that lubricating oil caused to flow into oil passage hole 13 a within drive shaft 13 is supplied to first annular groove 20 a and second annular grooves 20 b, 20 b via an oil hole (not shown) formed in the radial direction of drive shaft 13. Hence, a clearance between the outer peripheral surface of drive shaft 13 and the inner peripheral surface of each of first and second journal surfaces (portion) 21 a, 21 b, 21 b is sufficiently lubricated. Thus, an irregular behavior of swing camshaft 18 due to the friction on the inner peripheral surface of each journal surface is not easy to occur. From this standpoint, the lift difference between the two engine valves becomes stable. As an alternative of the first embodiment, the transmitting mechanisms whose lengths are different from each other are selectively assembled onto swing shaft 18 for the respective cylinders on the basis of the inner diameter of the inserting hole 18 a of swing camshaft 18 to make the lift difference between the two engine valves (two intake valves 2 a, 2 b) which is involved in the radial inclination of swing camshaft 18 with respect to the supporting shaft (drive shaft 13) uniform between each of the cylinders.

FIG. 8 shows a second preferred embodiment of the valve mechanism according to the present invention. In the second embodiment, in addition to the selective assembly of swing cam assembly 17 (or swing camshaft 18) as described in the first embodiment, a lift adjustment mechanism 30 is provided in the transmitting mechanism. Lift adjustment mechanism 30 in the second embodiment has the same structure as described in a Japanese Patent Application First Publication (tokkai) 2006-105082 published on Apr. 20, 2006.

Herein, a rough explanation of lift adjustment mechanism 30 will be made. This lift adjustment mechanism 30 includes: an approximately rectangular block shaped coupling portion 31 integrally installed on a tip portion of other end portion 23 b of rocker arm 23; a fixing female screw hole, formed in an inner part of coupling portion 31, extended from an upper surface thereof in a gravity direction of coupling portion 31, and on which a fixing screw member 32 is screwed from an upper direction of coupling portion 31; a pin inserting hole penetrated from both side surfaces of coupling portion 31, extended in a direction orthogonal to the fixing female screw hole, and through which a supporting hole 33 is inserted; and a shim inserting hole 35 fitted in a direction orthogonal to the female screw hole and to the pin inserting hole which is an axial direction of rocker arm 23 from a front surface side of coupling portion 31 and through an inner part of which an adjustment shim 34 is inserted.

A length of above-described adjustment shim 34 is set to be larger (longer) than a depth of shim inserting hole 35 and is formed for an operator to grasp a front end portion thereof projected from the shim inserting hole 35 to enable an easiness in a pulling-out-and-inserting exchange (replacement) of adjustment shim 34. It should be noted that this adjustment shim 34 is prepared by a plurality of shims having different depths of arc surfaces.

Then, when the respective structural members (components) of the valve mechanism are assembled, in order to adjust the valve lift quantities of respective intake valves 2 a, 2 b, first, an optimum adjustment shim 34 is selected from the plurality of the prepared shims, is inserted into shim inserting hole 35, and is interposed between above-described supporting pin 33 and its opposing member. Thereafter, fixing screw member 32 is inserted into fixing female screw hole from the upper side with respect to the gravity direction and is tightened thereto. That is to say, supporting pin 33 is grasped between adjustment shim 34 and fixing screw member 32 so that a position of an axial supporting point of link rod 25 is substantially modified. Thus, the lift quantity of each of intake valves 2 a, 2 b can be adjusted.

Hence, according to the second embodiment, first, after, as described in the first embodiment, the selective assembling of swing cam assembly 17 is carried out to make the lift difference of each intake valve 2 a, 2 b uniform between each of the cylinders, adjustment shim 34 is selectively adjusted for an average lift value Ya in the low engine revolution area of each of intake valves 2 a, 2 b in the same cylinder to be made uniform between each of the cylinders. That is to say, according to description contents of FIGS. 7A through 7D′, lift adjustment mechanism 30 adjusts average lift values Ya1, Ya2 of each of intake valves 2 a, 2 b in the first and second cylinders and, thereafter, adjusts an average lift value Ya3′ in the third cylinder. It should be noted that this adjusted average lift value may be average lift value Ya in the low engine revolution area or may be another average lift value Za in the high engine revolution area. In other words, average lift value Ya in the low engine revolution area may be a minor value since a force of link rod 25 compressed according to the spring loads of valve springs 3 a, 3 b is minor (weak) and average lift value Za in the high engine revolution area is a major value since the force extended by link rod 25 to be pressed due to the inertia load of the cam nose portion of each of first and second swing cams 19 a, 19 b is large. However, either average lift value Ya in the low engine revolution area or average lift value Za in the high engine revolution area may be referenced.

FIG. 9 shows a flowchart representing a procedure of a lift adjustment operation during the assembling of respective components into the valve mechanism in the second embodiment of the valve mechanism according to the present invention. First, at a step S1, clearance ΔD is measured by the operator using an instrument such as a vernier caliper from the equation of inner diameter E of inserting hole 18 a of swing camshaft 18 for each cylinder—outer diameter F of drive shaft 13 for each cylinder.

Next, at a step S2, a determination is made as to whether the difference of clearance ΔD between each of the cylinders is equal to or longer (larger) than a predetermined value. If the difference is smaller than the predetermined value, the routine goes to a step S4. If the difference of clearance ΔD is equal to or larger than the predetermined value, the routine goes to a step S3.

At this step S3, in order to make clearance ΔD between each cylinder uniform, for at least one cylinder, as described before, swing cam assembly 17, namely, one of swing cam assemblies 17 which has a different inner diameter E of inserting hole 18 a of swing camshaft 18 from any other swing cam assemblies 17 is selected and assembled. This causes the dispersion between the respective cylinders on the lift difference between both of intake valves 2 a, 2 b to be decreased.

At step S4, average lift values Ya (or Za) of both intake valves 2 a, 2 b in the respective cylinders are measured. At the next step S5, a determination as to whether each of the dispersion (difference) of average lift values Ya (or Za) between the respective cylinders is equal to or larger than another predetermined value is made.

It should be noted that, if the dispersion of average lift values Ya (or Za) between each of the cylinders is smaller than the other predetermined value, engine valve lifts (lift quantities) are approximately coincident with each other for all cylinders and the engine valve lifts at the sides of link rod 25 are approximately coincident with each other. Thus, the routine is directly returned. However, if the determination is made that the dispersion described above is equal to or larger than the other predetermined value, the routine goes to a step S6.

At step S6, average lift value Ya (or Za) of both intake valves 2 a, 2 b for a particular cylinder in which average lift value Ya is larger than average lift value Ya of any other cylinders is adjusted by means of lift adjustment mechanism 30 or average lift value Ya (or Za) for another particular cylinder in which its average lift value is smaller than average lift values Ya (or Za) of any other cylinders is adjusted by means of corresponding lift adjustment mechanism 30. Then, absolute values of the lift quantities between all cylinders are made coincident with each other and the routine is ended.

Hence, in the second embodiment, other than the selective assembly of swing cam assembly 17, namely, other than the adjustment of the lift differences between the two valves for the respective cylinders, lift adjustment mechanism 30 can adjust absolute values of average lift values Ya (or Za) between two intake valves 2 a, 2 b for all cylinders. Hence, it becomes possible to further reduce the dispersions of the combustion between the respective cylinders and of intake air charging efficiency between each of the cylinders. It should be noted that, as lift adjusting means (a lift adjusting section), any one of mechanisms in which distances between two holes of link rod 25 are different may selectively be assembled.

FIGS. 10A and 10B integrally show a third preferred embodiment of the valve mechanism according to the present invention. In addition to the selective assembly of swing cam assembly 17 as described in the first embodiment makes uniform their respective clearances ΔD between the respective cylinders and, intentionally, only the lift quantity for first swing cam 19 a at link rod 25 side is increased.

That is to say, as shown in FIGS. 7A′ through 7D′, the lift difference between both of intake valves 2 a, 2 b due to the inclination of swing camshaft 18 in the high engine revolution area occurs. Thus, a swirl of air mixture fuel at a suction stroke of the engine is developed. Consequently, a charging efficiency of fresh air is reduced, an engine knocking becomes easy to occur, and an output (power) has a tendency of reduction.

Therefore, in the third embodiment, a profile of first swing cam 19 a whose lift quantity is reduced due to the inclination of swing camshaft 18 in the high engine revolution area is formed to be relatively large so that the lift quantity of corresponding intake valve 2 a at one of the pair of intake valves 2 a, 2 b is set to become accordingly large. Thus, as shown in FIG. 10B, the lift difference between both of intake valves 2 a, 2 b due to an increase in a cam lift quantity of first swing cam 19 a and the lift difference between both of intake valves 2 a, 2 b due to the inclination of swing camshaft 18 in the clockwise direction become almost eliminated in the high engine revolution area. Hence, a sufficient suppression of the development in the intake swirl in the high engine revolution area can be made so that the technical problem of reduction in the charging efficiency in fresh air and the easy occurrence of engine knocking can be eliminated.

On the other hand, in the low engine revolution area, as described above, the inclination direction of swing camshaft 18 is reversed. As shown in FIG. 10A, the lift difference between both of intake valves 2 a, 2 b due to the increase in the profile of first swing cam 19 a and the lift difference between both intake valves 2 a, 2 b due to the inclination of the counterclockwise directional inclination of swing camshaft 18 become large.

Hence, an intake air swirl is sufficiently developed and the fuel combustion can, furthermore, be improved, and improvements in fuel consumption and exhaust emission can be achieved.

FIGS. 11A and 11B show a fourth preferred embodiment of the valve mechanism according to the present invention. In the fourth embodiment, as a measure of a slight enlargement of the lift quantity of one of the intake valves 2 a, 2 b which corresponds to first swing cam 19 a as described in the third embodiment, a cam clearance ΔC1 between a cam surface 22 a of first swing cam 19 a and an upper surface of first valve lifter 16 a is set to be smaller than a cam clearance ΔC2 between cam surface 22 b of second swing cam 19 b and the upper surface of second valve lifter 16 b.

Hence, in this embodiment, even if the cam profiles of respective cam surfaces 22 a, 22 b of respective swing cams 19 a, 19 b are set to be the same, it is possible to slightly enlarge the lift quantity of one of pair of intake valves 2 a, 2 b which corresponds to first swing cam 19 a. Hence, the same action and advantages as those in the third embodiment can be achieved.

FIG. 12 shows a fifth preferred embodiment of the valve mechanism according to the present invention. In the fifth embodiment, a lash adjuster 50 is provided for adjusting the cam clearances between the cam surfaces 22 a, 22 b of respective swing cams 19 a, 19 b and respective valve lifters 16 a, 16 b to be zero.

That is to say, as described in the first through third embodiments, the lift difference and the average lift value between both of intake valves 2 a, 2 b are dispersed in a case where the cam clearances between respective swing cams 19 a, 19 b and respective valve lifters 16 a, 16 b are dispersed, even if the inclinations of swing camshaft 18 are adjusted between each of the cylinders.

Therefore, as the structure described in FIG. 12 (for example, refer to a Japanese Patent Application First Publication (tokkai) 2003-172113 published on Jun. 20, 2003), lash adjuster 50 to adjust the cam clearances between respective swing cams 19 a, 19 b and respective valve lifters 16 a, 16 b to be zero is installed in an inner part of each of valve lifters 16 a, 16 b.

This permits the elimination of the dispersion of the cam clearances between respective swing cams 19 a, 19 b and respective valve lifters 16 a, 16 b. Thus, it becomes possible to improve lift accuracies of the lift difference and the average lift value described in each of the first through third embodiments. Consequently, the dispersion of the lift difference between the pair of intake valves 2 a, 2 b can, furthermore, be reduced between the respective cylinders.

It should be noted that lash adjuster 50 described above may, for example, be installed in an inner part of a pivot installed at one end portion of a swing arm interposed between respective swing cams 19 a, 19 b and a stem end of each intake valve 2 a, 2 b. For example, the structure of lash adjuster described in a Japanese Patent Application Publication No. 2003-155906 published on May 30, 2003 may be applied.

In addition, as a sixth preferred embodiment, suppose that both of the clearance (ΔD) between inner diameter E of inserting hole 18 a and outer diameter F of drive shaft 13 and cam clearances (ΔC) between cam surfaces 22 a, 22 b of respective swing cams 19 a, 19 b and the upper surfaces of respective valve lifters 16 a, 16 b are zeroes. On the basis of this supposition, in the sixth embodiment, the cam profiles of cam surfaces 22 a, 22 b of swing cams 19 a, 19 b are set to make lift difference (ΔY or ΔZ) between respective intake valves 2 a, 2 b approximately constant irrespective of the rotational angle of control shaft 32.

FIG. 13 shows representative valve lift characteristics for respective intake valves 2 a, 2 b through respective swing cams 19 a, 19 b in a case where the above-described cam profiles are set for cam surfaces 22 a, 22 b of respective swing cams 19 a, 19 b. Solid lines in FIG. 13 denote theoretical lift characteristics through first swing cam 19 a. Dot lines in FIG. 13 denote other theoretical lift characteristics through second swing cam 19 b. It should be noted that the theoretical lift characteristics are theoretical valve lift characteristics through respective cam profiles in a case where both of clearances ΔD and ΔC described above are supposed to be zero. Then, the above-described cam profiles are set for both theoretical lift differences Δ1, Δ2, and Δ3 to be approximately equal to each other in their peak lift ranges in cases where the valve lift characteristics are at a maximum lift, at an intermediate lift, and at a minimum lift, respectively.

Hence, according to the sixth embodiment, the lift differences of both of intake valves 2 a, 2 b provide approximately constant of Δ1≈Δ2≈Δ3. Therefore, even if the lift quantities in a case where clearances ΔD and ΔC are taken into consideration, the lift differences of pair of intake valves 2 a, 2 b can be maintained irrespective of control lift quantities in a case where control shaft 32 is twisted. Therefore, a favorable combustion state can be obtained even in a case of any of engine driving conditions.

FIG. 14 shows characteristic graphs with a lateral axis thereof taken along an angle of control shaft 32 and with a longitudinal axis thereof taken along a valve lift quantity. In a case where the control lift is varied by twisting control shaft 32, an upper solid line denotes a variation of a theoretical lift of one of pair of intake valves 2 a, 2 b corresponding to link rod 25 and a lower dot line denotes the variation of the theoretical valve lift of the other of the pair of intake valves 2 a, 2 b which corresponds to an opposite side to link rod 25. It should be noted that, if Δ1≈Δ2≈Δ3, the same lift difference can be maintained irrespective of control lift quantities.

It is also possible to modify the cam profiles of respective swing cams 19 a, 19 b so that peak lift difference Δ1 at the time of a minimum peak lift is maximized and peak differences Δ2, Δ3 during the intermediate lift and during the maximum lift are set to be approximately the same (Δ1>Δ2≈Δ3). These settings permit a sufficient swirl to be developed in the low engine revolution area, the combustion becomes favorable, and fuel consumption and exhaust emission performance are improved. If such a Δ1 of peak lift difference at the time of the minimum lift as described above is expressed to be Δ1′, a dot-and-dash line in FIG. 14 corresponds to a valve lift of one of pair of intake valves 2 a, 2 b which corresponds to the opposite side to link rod 25.

Furthermore, if the cam profiles are modified and are set to be such a relation of Δ1>Δ2>Δ3, the swirl is sufficiently developed even in a steady-state driving region which corresponds to the intermediate lift and the combustion can favorably be improved.

The present invention is not limited to the structure of each of the above-described preferred embodiments. The structure can arbitrarily be modified in a range where a technical idea of the invention is not modified.

Furthermore, the present invention is applicable to both valve sides or the exhaust valve side other than the intake valve side. The varying mechanism is not always limited to that of the above-described embodiments. A follower which opens or closes the engine valve may be a bucket type shown in the drawings or may be a swing arm type. In addition, the number of engine cylinders to which the present invention is applicable may be the multi-cylinder engine such as a four-cylinder engine or straight (in-line) six-cylinder engine.

Technical ideas grasped from the above-described preferred embodiments will be explained below. (1) The valve mechanism for the multi-cylinder engine as claimed in claim 1, wherein a lift adjusting section (lift adjusting means) configured to adjust simultaneously lift quantities of the two engine valves is installed in the transmitting mechanism.

According to the above-described invention of item (1), in addition to the feature that the lift difference of the two engine valves can be made uniform between each of the cylinders by the selection of the swing camshaft (swing cam assembly 17), the lift adjusting section (lift adjusting means) can make average lift values of the pair of engine valves uniform between each of the cylinders. Hence, the dispersions of combustion between each of the cylinders and of the intake air charging efficiency therebetween can, furthermore, be reduced. (2) The valve mechanism for the multi-cylinder internal combustion engine as claimed in claim 1, wherein the valve mechanism further comprises a lift adjustment mechanism configured to adjust an average lift quantity of lift quantities of the two engine valves or the lift quantity or a lift position of at least one of the two engine valves after the swing camshaft is selectively assembled to adjust the radial inclination of the swing camshaft between each of the cylinders to a predetermined value. (3) The valve mechanism for the multi-cylinder internal combustion engine as claimed in claim 1, wherein a cam lift quantity of one of the two swing cams is set to be larger than the cam lift quantity of the other of the two swing cams.

According to the invention described in item (3), in addition to the feature that the lift difference between the two engine valves can properly be made uniform between each of the cylinders, the lift differences of the two engine valves for the respective cylinders are expanded (enlarged) in the low engine revolution area to strengthen the swirl of air mixture fuel and a combustion level itself is improved. In the engine high revolution area, the lift differences between the two engine valves for the respective cylinders are shrunken (decreased) to reduce the swirl of air mixture fuel. Thus, an output (power) of the engine can be improved.

-   (4) The valve mechanism for the multi-cylinder internal combustion     engine as claimed in claim 1, wherein a cam clearance for one of the     two swing cams is set to be smaller than that for the other of the     two swing cams.

According to the invention described in item (4), as described in the above-described item (3), the valve lift of the one of the two engine valves can be set to be large without provision of the cam lift difference for the two swing cams.

-   (5) The valve mechanism for the multi-cylinder engine as claimed in     claim 1, wherein the valve mechanism further comprises a lash     adjuster configured to adjust a cam clearance to be zero is     interposed between the two swing cams and the two engine valves     corresponding to the two swing cams.

The lift difference between the two engine valves is also varied according to the dispersion in the respective cam clearances. However, if the lash adjuster is used, these can be maintained at a constant value or at zero. Hence, a lift accuracy is improved so that the dispersion of the lift difference between the two engine valves can, furthermore, be reduced.

-   (6) The valve mechanism for the multi-cylinder internal combustion     engine as claimed in claim 1, wherein a supporting shaft swingably     supporting the swing camshaft is the drive shaft.

Since the drive shaft serves as the supporting shaft, the drive shaft is revolved to stabilize a lubricating state between the outer peripheral surface of the drive shaft and the swing cam and, thereby, an inclination behavior of the swing camshaft becomes stable. Hence, the lift difference between the two engine valves becomes stable and the dispersion of the lift difference between the two engine valves is reduced between each of the cylinders.

-   (7) The valve mechanism for the multi-cylinder internal combustion     engine as claimed in claim 1, wherein the valve mechanism further     comprises a control valve configured to vary a posture of the     transmitting mechanism when it is revolved to simultaneously vary     lift quantities of the pair of engine valves.

The revolution of the control shaft permits a variable control of the valve lift quantities in accordance with the engine driving condition. Hence, the lift difference between the two engine valves becomes stable. Consequently, various performances of the engine are improved and a stabilization of engine revolutions can be achieved.

-   (8) The valve mechanism for the multi-cylinder internal combustion     engine as claimed in item (7), wherein cam profiles of the swing     cams are set in order for a difference in the lift quantities of the     two engine valves when both of a clearance between an outer     peripheral surface of the supporting shaft and an inner peripheral     surface of the inserting hole of the swing camshaft and a cam     clearance on the two swing cam are supposed to be zero to fall     within a predetermined range irrespective of the rotational angle of     the control shaft.

According to the invention described in item (8), the lift difference of the two engine valves is maintained within the predetermined range irrespective of any of the controlled lift quantities of the respective engine valves. Hence, the favorable combustion state can be obtained.

This application is based on a prior Japanese Patent Application No. 2006-278211. The entire contents of a Japanese Patent Application No. 2006-278211 with a filing date of Oct. 12, 2007 are hereby incorporated by reference. Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims. 

1. A valve mechanism for a multi-cylinder internal combustion engine, comprising: a drive shaft rotationally driven by means of a crankshaft of the engine and on an outer periphery of which a drive cam is installed; a swing camshaft swingably and axially supported on an outer periphery of a supporting shaft via an inserting hole thereof with a predetermined clearance and on outer peripheries of axial both end portions of which two swing cams per cylinder are installed; two engine valves operated to be open and closed by taking swing motions of the two swing cams via the swing camshaft; and a transmitting mechanism linked to one axial end portion of the swing camshaft to convert a rotational motion of the drive cam into the swing motion to transmit the swing motion to the two swing cams, wherein the swing camshaft is selectively assembled for each of the cylinders on the basis of at least an inner diameter of the inserting hole to make a lift difference between the two engine valves which is involved in a radial inclination of the swing camshaft with respect to the supporting shaft uniform between each of the cylinders.
 2. The valve mechanism for the multi-cylinder internal combustion engine as claimed in claim 1, wherein a lift adjusting section configured to simultaneously adjust lift quantities of the two engine valves is installed in the transmitting mechanism.
 3. The valve mechanism for the multi-cylinder internal combustion engine as claimed in claim 1, wherein the valve mechanism further comprises a lift adjustment mechanism configured to adjust an average lift quantity of lift quantities of the two engine valves or the lift quantity or a lift position of at least one of the two engine valves after the swing camshaft is selectively assembled to adjust the radial inclination of the swing camshaft between each of the cylinders to a predetermined value.
 4. The valve mechanism for the multi-cylinder internal combustion engine as claimed in claim 1, wherein a cam lift quantity of one of the two swing cams is set to be larger than that of the other of the two swing cams.
 5. The valve mechanism for the multi-cylinder internal combustion engine as claimed in claim 1, wherein a cam clearance of one of the two swing cams is set to be smaller than that of the other of the two swing cams.
 6. The valve mechanism for the multi-cylinder internal combustion engine as claimed in claim 1, wherein the valve mechanism further comprises a lash adjuster interposed between the two swing cams and the two engine valves corresponding to the two swing cams to adjust a cam clearance to be zero.
 7. The valve mechanism for the multi-cylinder internal combustion engine as claimed in claim 1, wherein the supporting shaft on which the swing camshaft is swingably and axially supported is the drive shaft.
 8. The valve mechanism for the multi-cylinder internal combustion engine as claimed in claim 1, wherein the valve mechanism further comprises a control shaft configured to vary a posture of the transmitting mechanism when it is revolved to simultaneously vary lift quantities of the two engine valves.
 9. The valve mechanism for the multi-cylinder internal combustion engine as claimed in claim 8, wherein cam profiles of the two swing cams are set in order for a difference in the lift quantities of the two engine valves when both of a clearance between an outer peripheral surface of the supporting shaft and an inner peripheral surface of the inserting hole of the swing camshaft and a cam clearance on the two swing cams are supposed to be zero, respectively, to fall within a predetermined range irrespective of a rotational angle of the control shaft.
 10. An assembling method of a valve mechanism for a multi-cylinder internal combustion engine, the valve mechanism comprising: a drive shaft rotationally driven by means of a crankshaft of the engine and on an outer periphery of which a drive cam is installed; a swing camshaft swingably and axially supported on an outer periphery of a supporting shaft via an inserting hole thereof with a predetermined clearance and on outer peripheries of axial both end portions of which two swing cams per cylinder are installed; two engine valves operated to be open and closed by taking swing motions of the two swing cams via the swing camshaft; and a transmitting mechanism linked to one axial end portion of the swing camshaft to convert a rotational motion of the drive cam into the swing motion to transmit the swing motion to the two swing cams, and the assembling method comprising: measuring an outer diameter of the supporting shaft and an inner diameter of the inserting hole of the swing camshaft; and selectively assembling the swing camshaft for each of the cylinders on the basis of the measured inner diameter of the inserting hole to make a lift difference between the two engine valves which is involved in a radial inclination of the swing camshaft with respect to the supporting shaft uniform between each of the cylinders.
 11. An assembling method of a valve mechanism for a multi-cylinder internal combustion engine, the valve mechanism comprising: a drive shaft rotationally driven by means of a crankshaft of the engine and on an outer periphery of which a drive cam is installed; a swing camshaft swingably and axially supported on an outer periphery of a supporting shaft via an inserting hole thereof with a predetermined clearance and on outer peripheries of axial both end portions of which two swing cams per cylinder are installed; two engine valves operated to be open and closed by taking swing motions of the two swing cams via the swing camshaft; and a transmitting mechanism linked to one axial end portion of the swing camshaft to convert a rotational motion of the drive cam into the swing motion to transmit the swing motion to the two swing cams, and the assembling method comprising: measuring an outer diameter of the supporting shaft and an inner diameter of the inserting hole of the swing camshaft; and selectively assembling the transmitting mechanisms whose lengths are different from each other onto the swing camshaft for the respective cylinders on the basis of the measured inner diameter of the inserting hole to make a lift difference between the two engine valves which is involved in a radial inclination of the swing camshaft with respect to the supporting shaft uniform between each of the cylinders.
 12. The assembling method of the valve mechanism for the multi-cylinder internal combustion engine as claimed in claim 11, wherein the assembling method further comprises adjusting an average lift quantity of lift quantities of the two engine valves or a lift quantity or a lift position of at least one of the two engine valves to a predetermined value through a lift adjustment mechanism installed in the transmitting mechanism after the radial inclination of the swing camshaft with respect to the supporting shaft is made uniform between each of the cylinders in the selective assembling of the transmitting mechanisms. 